Use TrustedSocketFactory for STARTTLS.

The TrustedSocketFactory, which provides goodies like better cipher suites and
TLSv1.2, was only being used for tunnelled connections.  Use it for STARTTLS
connections as well.
Update Polish translation

new strings + one typo
Update Czech translation
Update Russian translation
Update Greek translation
Update Hungarian translation
Clean up Hungarian translation
Merge branch 'translations'
Recreate app icon from SVG file

Add higher resolution icons so K-9 looks snazzy on newer devices.
Merge pull request #417 from bk2204/tsf-starttls

Use TrustedSocketFactory for STARTTLS
Fix contact picture color generation.

Make sure to return different colors for senders with different name,
but the same mail address (e.g. mails sent by certain issue tracking
systems).